Enzymatic polyethylene terephthalate degradation using a genetically stabilized cutinase immobilized on magnetic nanoparticles.

The enzymatic depolymerization of polyethylene terephthalate (PET) is an alternative recycling method that enables PET to be converted into monomers, which can be repeatedly used to synthesize new plastics without losing their mechanical properties. In this work, superparamagnetic iron oxide nanoparticles (SPIONs) were synthesized, subsequently coated with silica, aminated, and activated with glutaraldehyde to serve as supports for the immobilization of a thermostable mutant of cutinase, Cut190∗∗SS. This biocatalyst (SPIONs-GLU-Cut190∗∗SS) was employed in the depolymerization of PET into terephthalic acid (TPA), mono-(2-hydroxyethyl) terephthalic acid (MHET) and bis-(2-hydroxyethyl) terephthalate (BHET), and a Central Composite Rotatable Design (CCRD) was performed to optimize the reaction conditions. The immobilization allowed the enzyme to maintain almost unaltered activity and improved its stability. Under optimized conditions (biocatalyst percentage of 6.50 % (w/v) and PET concentration of 50 mg/mL, 48 h of reaction at 70 °C), the biocatalyst SPIONs-GLU-Cut190∗∗SS generated 13.45 ± 0.87 μmol of total monomers resulting in PET depolymerization yield of 10.10 %, i.e., a 6-fold increase in monomer generation performance compared to that found using a similar amount of free cutinase. Alternative strategies for immobilization should be explored to further improve the depolymerization of PET into monomers.